Medical installation tool

ABSTRACT

An installation tool that is useful for the efficient and effective placement of an article, such as an artificial disc, between adjacent vertebral bodies is provided. The installation tool can be provided as a kit having modular components which allow the surgeon to select from among a variety of components to assemble an installation tool that is optimized for its intended use. The installation tool of the invention generally includes a pair of opposed levers, each of which has a proximal handle portion and a distal portion. A fulcrum is disposed between the two levers to enable proper operation of the tool. The tool further includes a pusher block that is positioned between the two levers and is selectively movable between an initial location distal of the fulcrum and a final location adjacent the distal end of the levers. The pusher block includes a proximal end, a distal end, and a bore extending at least partially therethrough. A pusher rod, which facilitates movement of a pusher block, has a distal end extending into the bore in the pusher block and a proximal, handle end.

CROSS-REFERENCE TO RELATED APPLICATIONS

This applicationMore than one reissue application has been filed for thereissue of U.S. Pat. No. 6,755,841. This application is a continuationreissue of U.S. patent application Ser. No. 14/172,631, filed on Feb. 4,2014, now U.S. Pat. No. Re. 45,639,which is a continuation reissue ofU.S. patent application Ser. No. 13/331,675, filed on Dec. 20, 2011, nowU.S. Pat. No. Re. 44,835, which is a continuation reissue of U.S. patentapplication Ser. No. 11/397,887, filed on Mar. 29, 2006, now U.S. Pat.No. Re. 43,317, which is a reissue of U.S. patent application Ser. No.10/011,264, filed on Dec. 7, 2001, now U.S. Pat. No. 6,755,841, which isa continuation-in-part of U.S. patent application Ser. No. 09/566,514,filed on May 8, 2000, now U.S. Pat. No. 6,478,800 entitled “MedicalInstallation Tool,” the entire contents of each of which is herebyexpressly incorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates to a tool for inserting prostheses within thebody, and more particularly to tools for inserting prostheses, such asartificial discs and cages, within an intervertebral space.

Spinal surgery involves many challenges as the long-term health andmobility of the patient often depends on the surgeon's technique andprecision. One type of spinal surgery involves the removal of thenatural disc tissue that is located between adjacent vertebral bodies.Procedures are known in which the natural, damaged disc tissue isreplaced with an interbody cage or fusion device, or with a discprosthesis.

The insertion of an article, such as an artificial disc prosthesis,presents the surgeon with several challenges. The adjacent vertebralbodies collapse upon each other once the natural disc tissue is removed.These bodies must be separated to an extent sufficient to enable theplacement of the prosthesis. However, if the vertebral bodies areseparated, or distracted, to beyond a certain degree, further injury canoccur. The disc prosthesis must also be properly positioned between theadjacent vertebral bodies. Over-insertion, or under-insertion of theprosthesis can lead to pain, postural problems and/or limited mobilityor freedom of movement.

Specialized tools have been developed to facilitate the placement ofdevices, such as disc prosthesis, between adjacent vertebral bodies of apatient's spine. Among the known tools for performing such proceduresare separate spinal distractors and insertion devices. The use ofseparate tools to distract the vertebral bodies and insert a discprosthesis or graft can prove cumbersome. Further, the use of somedistractors can cause over-distraction of the vertebral bodies.

Exemplary devices for installing prosthesis and/or grafts betweenvertebral bodies are disclosed in U.S. Pat. Nos. 5,431,658 and5,505,732. U.S. Pat. No. 5,431,658 discloses a facilitator device forthe insertion of bone grafts between two adjacent vertebrae. Thedisclosed tool has two flat, tong-like guides that distract thevertebrae as a screw-type inserter forces the graft between thedistracted vertebrae. U.S. Pat. No. 5,505,732 discloses an apparatus anda method of inserting spinal implants. The intervertebral space is firstdistracted and a hollow sleeve having teeth at one end is then driveninto the vertebrae that are adjacent the disc space. A drill is thenpassed through the hollow sleeve, removing the disc and the bone inpreparation for receiving the spinal implant, which is then insertedthrough the sleeve.

Despite existing tools and technologies, there remains a need to providea device to facilitate the proper and convenient insertion of an object,such as a disc prosthesis, between adjacent vertebral bodies whileminimizing the risk of further injury to the patient.

SUMMARY OF THE INVENTION

The present invention provides a device useful for implantingprostheses, such as artificial spinal discs and cages, within a patientin a safe and efficient manner. The installation tool of the inventiongenerally includes a pair of opposed levers, each of which has aproximal handle portion and a distal portion. A fulcrum is disposedbetween the two levers to enable proper operation of the tool. The toolfurther includes a pusher block that is positioned between the twolevers and is selectively movable between an initial location distal ofthe fulcrum and a final location adjacent the distal end of the levers.The pusher block includes a proximal end, a distal end, and a boreextending at least partially therethrough. A pusher rod, whichfacilitates movement of a pusher block, has a distal end extending intothe bore in the pusher block and a proximal, handle end.

The pusher rod and/or pusher block can be adapted to mate to a varietyof prosthesis devices. In one embodiment, the pusher block can include ablind bore and a distal end of the pusher rod can mate with the blindbore in the pusher block. The pusher block can thus include a distallyfacing surface having surface features adapted to conform to or matewith complementary surface features on a prosthesis. In anotherembodiment, the bore can extend entirely through the pusher block toallow a distal end of the pusher rod to extend through the bore in thepusher block. The pusher rod can thus include a distal tip that iseffective to mate to a prosthesis.

In yet another embodiment, the rod can include a first externallythreaded distal portion and a second externally threaded distal portion.The second distal portion is positioned proximal to the first distalportion, and has a diameter greater than a diameter of the first distalportion. The bore of the pusher block can include a threaded proximalopening, a distal opening, and a chamber formed therebetween. Theproximal opening is threadingly matable with the second distal portionof the rod to allow the second distal portion of the rod to bethreadingly inserted through the proximal opening and positioned withinthe chamber. The diameter of the distal opening of the pusher blockshould be less than the diameter of the proximal opening of the pusherblock to prevent the second threaded portion of the rod from extendingthrough the distal opening in the pusher block. The threaded seconddistal portion is preferably freely rotatable within the chamber of thepusher block. The threaded first distal portion of the rod extendsthrough the distal opening in the pusher block and includes a distal tipwhich is adapted to mate to a prosthesis.

In other aspects of the invention the bore extends entirely through thepusher block and a distal tip of the pusher rod is adapted to extendthrough the bore in the pusher block. The distal tip of the pusher rodis further adapted to mate to a grasping element effective to releasablyengage a prosthesis. The grasping element can include an elongateproximal portion with a bore formed therein and a distal portion that iseffective to releasably engage a prosthesis. The proximal portion has anouter diameter that is adapted to fit within the bore of the distal endof the pusher block. The distal portion of the grasping can includeopposed first and second components that are movable between a first,open position, and a second, closed position that is effective to engagea prosthesis. In use, the distal end of the rod threadingly engages thebore of the grasping element. Rotation of the rod in a first directionis effective to cause the elongate proximal portion of the graspingelement to move proximally within the bore of the pusher block, therebymoving the first and second components to the second, closed position.Rotation of the rod in a second, opposed direction is effective to causethe elongate proximal portion of the grasping element to move distallyout of the bore of the pusher block and move the first and secondcomponents to the first, open position. The first and second componentscan optionally include at least one surface feature effective to engagea prosthesis.

In yet another embodiment, a medical device installation kit can beprovided having a pair of opposed levers, a fulcrum disposed between thelevers for allowing pivotal movement of the levers with respect to eachother, and a plurality of prosthesis installation assemblies. Eachassembly is adapted to be slidably disposed between the levers andmovable between a first, proximal position and a second, distal portion.A handle portion can be provided on each assembly for moving theprosthesis installation assembly between the first and second positions.Each assembly further includes a distal prosthesis effecting elementadapted to place a prosthesis between adjacent bone structures.

In one embodiment, one of the prosthesis installation assembliesincludes a pusher block having a proximal end, a distal end, and a boreextending therethrough, a pusher rod slidably disposed between thelevers and extending through the bore in the pusher block, and agrasping element effective to releasably engage a prosthesis. In anotherembodiment, one of the prosthesis installation assemblies includes apusher rod having a proximal handle portion and a distal portion havinga distal tip adapted to positively engage a prosthesis. A pusher blockcan be provided having a bore extending therethrough and adapted toreceive a distal portion of the pusher rod. In yet another embodiment,one of the prosthesis installation assemblies can include a pusher rodhaving an externally threaded first distal portion and an externallythreaded second distal portion. The second distal portion has a diametergreater than the first distal portion, and is positioned proximal to thefirst distal portion. The assembly further includes a pusher blockhaving a bore extending entirely therethrough having a threaded proximalopening that is threadingly matable with the second distal portion ofthe rod, and a distal opening having a diameter less than the diameterof the second distal portion of the rod. A chamber having a diametergreater than the diameter of the second distal portion of the pusher rodis disposed between the first and second openings of the pusher block.In other aspects, one of the prosthesis installation assemblies caninclude a pusher block having a bore extending therethrough, a pusherrod extending through the bore in the pusher block, and a plurality ofconnector elements having a proximal portion adapted to mate to a distaltip of the pusher rod, and a distal portion adapted to mate to aprosthesis.

The installation tool of the invention can be used in the followingmanner. Once the natural, damaged disc tissue is removed from a patientand the area is prepared to receive an artificial prosthesis, such as anartificial disc, the artificial disc is loaded between the levers of theinstallation tool so that a posterior side of the disc abuts a distalend of the pusher block. The distal tip of the levers is then positionedbetween the vertebral bodies such that the outwardly facing surfaces ofeach lever contacts opposed vertebral bodies. Once this position isachieved, the pusher rod is advanced distally, causing the pusher blockand the artificial disc to likewise move distally along the innersurfaces of the levers. As the artificial disc and the pusher rod movedistally, or forward, the levers separate and also cause verticalseparation of the adjacent vertebral bodies. To achieve the properposition of the artificial disc, the distal facing surfaces of thepusher block should contact the vertebral bodies. Once such contact isachieved between the distal facing surfaces of the pusher block and thevertebral bodies, the artificial disc is properly positioned. This toolthus enables the proper positioning of the artificial disc between thevertebral bodies, without over-insertion or under-insertion of theartificial disc, while minimizing the degree of distraction of thevertebrae. To remove the tool, a slaphammer or similar device can beused to apply a proximally directed force to the tool to extract theblade tips without removing the implant.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a perspective view of an installation tool according to thepresent invention;

FIG. 2 is a side, elevation view of the tool shown in FIG. 1;

FIG. 3 is a top view of the tool shown in FIG. 1;

FIG. 3A is a perspective view of an installation tool having curveddistal blade tips according to another embodiment of the presentinvention;

FIG. 3B is a side view illustration of another embodiment of aninstallation tool according to the present invention;

FIG. 4 is a sectional view of the tool shown in FIG. 2, at line 4-4;

FIG. 5 is a top view of a portion of the tool shown in FIG. 2, at line5-5;

FIG. 6 is an exploded view of a proximal portion of the tool shown inFIG. 1;

FIG. 7 is an exploded view of a portion of the tool shown in FIG. 1;

FIG. 7A is an enlarged view of another embodiment of a pusher block ofthe tool shown in FIGS. 1-3B;

FIG. 8 is a side view of a portion of a medical installation toolaccording to yet another embodiment;

FIGS. 8A-8D illustrate, sequentially, the operation of the installationtool according to the present invention during the installation of anartificial disc;

FIG. 9 is a side-elevation view of one embodiment of an installationtool according to the present invention in an initial, unlockedposition;

FIG. 10 is a side view of the installation tool of FIG. 9 in a final,locked position;

FIG. 11 is a sectional view of the tool shown in FIG. 9, at line 11-11;

FIG. 12 is perspective view of a pusher block useful with the tool ofthe present invention;

FIG. 13 is a perspective view of a further embodiment of an installationtool according to the present invention;

FIG. 14 is an exploded, perspective view of a portion of theinstallation tool shown in FIG. 13;

FIG. 15A is a side, elevation view of a portion of the distal end of theinstallation tool of FIG. 13 in a first position;

FIG. 15B is a side, elevation view of a portion of the distal end of theinstallation tool of FIG. 13 in a second position;

FIG. 16 is an exploded side, perspective view of one embodiment of aconnector element for use with a medical installation tool;

FIG. 17 is an exploded perspective view of a slaphammer instrument foruse with a medical installation tool of the present invention;

FIG. 18 is a side view illustration of a portion of a pusher rod for usewith a medical installation tool according to the present invention;

FIG. 19A is a cross-sectional side view of a pusher block component ofthe medical installation tool shown in FIG. 8; and

FIG. 19B is a plan view of the proximal end of the pusher block of FIG.19A.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention provides an installation tool that is useful forthe efficient and effective placement of an article, such as anartificial disc or cage, between adjacent vertebral bodies. Theinstallation tool can be provided as a kit having modular componentswhich allow the surgeon to select from among a variety of components toassemble an installation tool that is optimized for its intended use.Although the invention is described primarily with reference to beingused to install an artificial disc between adjacent vertebral bodies, itis understood that the installation tool of the invention can be used toplace other elements between vertebral bodies, or in other locationswithin a patient's body. Exemplary elements that can be placed betweenvertebral bodies include, but are not limited to interbody cages,fulsion devices, spacers, grafts, and the like.

As shown in FIGS. 1-3B, the installation tool 10 of the inventionincludes opposed levers 12, 14, each having a distal portion 12A, 14Aand a proximal, handle portion 12B, 14B. Disposed between the levers 12,14 is a fulcrum 16 and pusher block 18, which is disposed distally ofthe fulcrum 16. The pusher block 18 includes a bore extending at leastpartially therethrough and it is selectively movable from an initialposition distal of the fulcrum 16 to a final location adjacent a distalend of the levers. A pusher rod 20, which facilitates selective movementof the pusher block, has a proximal handle end 20B and a distal end 20Aextending into the bore in the pusher block. Although not part of theinvention, a prosthesis, such as an artificial disc 24, is positionedbetween the levers, distal of the pusher block 18.

Preferably the levers 12 and 14 are elongate elements that are mirrorimages of each other. There is no absolute top or bottom of the tool 10since it is possible to use either surface as a “top” surface. For easeof reference, however, levers will sometimes be described herein withreference to an illustrated orientation. For example, lever 12, andcomponents thereof, may sometimes be referred to as the top, upper, orsuperior lever while lever 14 may sometimes be referred to as thebottom, lower, or inferior lever.

With further reference to FIGS. 1-3B, the levers 12, 14 include distal12A, 14A and proximal 12B, 14B ends. The proximal end 12B, 14B of eachlever may be of a shape that facilitates convenient grasping andhandling of the tool. The proximal end of each lever may compriseapproximately one-half of the length of each lever. In one embodiment, ashoulder 26 marks the end of the proximal portion of the tool and thebeginning of the distal portion of the tool. As shown in FIGS. 1 and 3,the proximal portion of each lever preferably has a width (W_(p)) thatis greater than the width (W_(d)) of the distal portion of each lever.

The proximal portion 12B of each lever may include an indented region 28for receiving the fulcrum 16. As shown in FIGS. 1 and 6, the indentedregion 28 is in the form of a substantially rectangular cut-out formedon both sides of levers 12B, 14B. This indented region 28 enables thelevers to conveniently seat the fulcrum 16, as described below. Therecessed region 28 is preferably formed slightly proximally of theshoulder 26. In one embodiment the distal portion of the recessed region28 begins approximately 10 to 100 mm proximally of shoulder 26. Therecessed region 28 generally has a length in the range of about 10 to 40mm and is recessed by about 1 to 40 mm.

The proximal region of each lever 12B, 14B may also include a bore 30A,30B which is adapted to seat a bolt 32 that enables control of thespacing between levers so that the pusher block accurately engages themetal portion of the artificial disc. As shown in FIG. 6, bolt 32includes a head 34 and shaft 35 having a threaded region 36. Preferably,internal threads 36 are formed within bore 30A.

The distal portion of each lever 12A, 14A features side surfaces 46, 48,outwardly facing surfaces 38, 40 (illustrated as top and bottom surfacesin FIG. 6, respectively), and inwardly facing surfaces 42, 44 upon whichthe artificial disc 24 can ride during an installation procedure. Theoutwardly and inwardly facing surfaces of the lever preferably aresubstantially smooth. The inwardly facing surfaces 42, 44 can, however,include surface features effective to mate to complementary surfacefeatures formed on the implant. For example, each lever 12, 14 caninclude a rail (not shown) formed in the inwardly facing surface 42, 44that is effective to be slidably disposed within a corresponding grooveor channel formed in the implant. As a result of the surface featuresformed on the inwardly facing surfaces 42, 44 of the levers 12, 14, thewidth (W_(d)) of the distal portion of each lever can be substantiallythe same as or even greater than the width (W_(p)) of the proximalportion of each lever.

The distal portions 12A, 14A of the levers 12, 14 can also have bladetips 50A, 50B formed at the distal ends of the levers. The blade tipsare sized and configured to facilitate their placement between vertebralbodies 201, 202. The outwardly facing surfaces 52A, 52B of blade tipsmay be configured to have surfaces that are beveled or radiused. In oneembodiment illustrated in FIG. 3A, the blade tips 12 _(c)C, 14 _(c)C canbe substantially curved or angled in a superior or inferior direction tofacilitate placement of the blade tips 12 _(c)C, 14 _(c)C betweenadjacent vertebrae. In the illustrated embodiment, the distal tip of therod 20 _(c) includes a spring 2 which allows the distal portion of therod 20 _(c) to conform or bend to the shape of the curved blade tips50A, 50B. The proximal end 4 of the spring 2 can be threadingly mated toor otherwise attached to the distal end of the rod 20 _(c), and the end6 of the spring 4 can be attached to the proximal end of the pusherblock 18 _(c). Preferably, the pusher block 18 _(c) includes aprotrusion adapted to extend into the bore in the spring 4 to mate thepusher block 18 _(c) to the spring 4.

The thickness of the levers, measured at the blade tips when the tool isclosed, as shown in FIG. 1, can be considerably less than the thicknessof the levers measured near the fulcrum between outwardly facingsurfaces 38, 40 when the tool is in the closed position. Preferably, thethickness measured at the blade tips is in the range of about 0.5 to 2mm. A portion of each lever 12A, 14A, disposed adjacent a proximal endof the blade tips 50A, 50B, can include a stop surface 54. The stopsurface 54, which is substantially vertically oriented and distallyfacing, is adapted to abut a vertebral body during a surgical procedurefor installing an element, such as an artificial disc, between adjacentvertebral bodies. The stop surface 54 may assume a variety ofconfigurations. In one embodiment, shown in FIGS. 2 and 8A-9, the stopsurface has a substantially concave profile when viewed in the verticalplane.

As shown in FIGS. 6-7 the side surfaces of the distal portions 12A, 14Aof the levers 12, 14 may have opposed rails 56, 58, with a recessedtrack 60 disposed therebetween. The formation of such recessed tracks 60within the distal side walls of levers 12, 14 causes these elements tohave a profile that, as shown in FIGS. 4 and 7, is substantiallyI-shaped or T-shaped. The rails 56, 58 and track 60, as discussed below,can be effective to facilitate smooth and efficient movement of thepusher block.

One of ordinary skill in the art will appreciate that the size and shapeof the levers may vary. Generally, however, the overall length of thelevers is about 200 to 400 mm, with proximal portion 12B, 14B (proximalend to shoulder 26) having a length of about 100 to 300 mm and thedistal portion 12A, 14A (shoulder 26 to blade tips) having a length ofabout 100 to 300 mm.

In one embodiment, illustrated in FIGS. 1-3 and 6, the fulcrum 16 issubstantially a block-like object having substantially vertical sidewalls 62. The upper and lower surfaces 64, 66 of fulcrum 16 includerecesses or grooves 68, each of which is defined by a base wall 70, 72and opposed inner side walls 74. A core section 78 lies between the basewalls 70 and 72. The core section 78 preferably includes a central bore80 to allow passage of pusher rod therethrough. In an exemplaryembodiment each base wall 70, 72 includes a mounting post 82. As shownin FIG. 6, a biasing element 84′, such as a coil spring, may be placedupon each of mounting posts 82 and the mounting posts, in turn,positioned within the bores 31A, 31B of levers 12, 14.

The fulcrum 16 may assume virtually any size and shape that is able torender it effective to separate a substantially intermediate portion oflevers while allowing the proximal, handle portion 12B, 14B to be closedtogether and result in the opening or separation of the distal portion12A, 14A. Generally, the height of the vertical side walls 62 is in therange of about 20 to 70 mm while the height of the core section 78(shown in FIG. 7) is in the range of about 5 to 30 mm. The length of thecore section 78 may be about 5 to 40 mm.

One of ordinary skill in the art will further appreciate that thefulcrum may take on a variety of other shapes, sizes and mountingconfigurations. The embodiment described above is intended to representone exemplary fulcrum design and mounting configuration.

The bolt 32, as noted above, can be used to adjust the height/spacing ofthe levers. One of bores 30A, 30B, has internal threads 37 that matewith threaded portion 36 of bolt 32. Tightening or loosening of the boltwill result in increasing or decreasing the spacing/distance between thelevers.

The pusher block 18, as illustrated in FIG. 7, may be in the form of asubstantially block-like object having vertical side walls 84 thatdefine upper and lower recesses 86, 88 wherein each recess is defined bya base wall 90 and opposed inwardly facing side walls 92. Each inwardlyfacing side wall 92 preferably includes a guide post 94 that is matablewithin recessed tracks 60 formed in the distal portion of levers 12A,14A.

In another embodiment, shown in FIG. 7A, each inwardly facing side wall92′ of pusher block 18 _(a) includes a rail 95 extending from theproximal end to the distal end of the pusher block 18 _(a). Each rail 95forms a groove or track 97 that is matable with rail 56 or rail 58 ofeach lever 12, 14. The rail 95 and track 97 of top and bottom sides ofthe pusher block 18 _(a) limit movement of the levers 12, 14 withrespect to each other. In use, proximal movement of the pusher block 18_(a) is effective to cause the blade tips 50A, 50B to move to the closedposition, and to cause the proximal portion of the levers 12, 14 to befully disposed within the recesses 68 (FIG. 6) of the fulcrum 16. Oncethe pusher block 18 is positioned just distal to the fulcrum 16, thelevers 12, 14 are in effect locked in the closed position.

Referring back to FIG. 7, the core section 91 of the pusher block 18 isdisposed between upper and lower base walls 90 and includes a proximallyfacing wall 96 and a distally facing wall 97. In one embodiment, theheight of the core section 91 is less than the height of the prosthesisto be installed, thus enabling inwardly facing surfaces 42, 44 of levers12, 14 to contact the prosthesis. Alternatively, as shown in FIG. 8, thecore section 91 can have a height h_(c) that is slightly greater thanthe height of the prosthesis 24 _(b) to prevent the prosthesis 24 _(b)from contacting the inwardly facing surface 42, 44 of each lever 12_(b), 14 _(b). Thus, the prosthesis 24 _(b) is spaced apart from thelevers 12 _(b), 14 _(b) when mated to the pusher block 18 _(b) or pusherrod 20 _(b). The distally facing wall of the pusher block 18 can have ashape which conforms to the shape of a prosthesis. In an exemplaryembodiment, several pusher blocks 18, 18 _(a), 18 _(b) can be provided,each having a different size and/or shape that is optimized for use witha particular prosthesis or patient.

As noted above, a pusher rod 20 may be utilized to actuate pusher block18. The pusher rod 20 is preferably an elongate, cylindrical memberhaving a proximal end 20B and a distal end 20A. The rod is adapted to bepositioned between the proximal ends 12B, 14B of the levers 12, 14 sothat it extends into or through the bore 80 in fulcrum 16. The rod 20can be adapted to mate to the pusher block 18 such that forward andrearward movement of the pusher rod will directly move the pusher block.Alternatively, the pusher block 18 can include a bore extending entirelytherethrough, and the rod 20 can be disposed through the bore to matedirectly to a prosthesis, or to mate to a connector element which, inturn, mates to a prosthesis.

The pusher rod 20 can optionally include a stop feature to prevent thelevers 12, 14 from being removed from the recessed formed in the pusherblock. As shown in FIGS. 3A and 3B, the rod 20, 20 _(c) can include astop surface 17 which abuts the proximal opening of the bore 80 in thefulcrum 16, thereby preventing proximal movement of the levers 12, 14and fulcrum 16. The stop surface 17 can be formed by a change indiameter of the pusher rod 20, 20 _(c), such that the proximal portionof the rod has a diameter greater than the distal portion of the rod 20,20 _(c), and greater than the bore in the pusher block 18.Alternatively, the stop surface 17 can be formed from an annular flangeor similar protruding structure.

The pusher block 18 and pusher rod 20 can include a variety of features,e.g. connector elements, for joining the block 18 to the rod 20, or formating the rod 20 and/or the block 18 to a prosthesis 24. By way ofnon-limiting example, FIG. 7 illustrates one embodiment in which theproximal end of the pusher block 18 facing wall includes a blind bore 98having internal threads 100. The threads are adapted to mate withcomplimentary threads 102 formed on a distal end 20A of the pusher rod20, thereby allowing the pusher rod 20 to positively engage the pusherblock 18. The distal facing wall 97 of the pusher block may include arecessed region 104 that is adapted to nest artificial disc 24. Asillustrated, the recessed region 104 has dimensions that enable theartificial disc to fit loosely therein. One of ordinary skill in the artwill appreciate that the recessed area should have dimensions slightlygreater than the dimensions of the disc so as to avoid a frictional fitthat may inhibit free release of the disc from the tool. FIG. 12illustrates one embodiment of a recessed region 104 having a contactwall 106 that has a generally arcuate shape. Preferably, contact wall106 is substantially concave and well suited to maintaining contact overa substantial surface area of a generally curved (convex) posteriorsurface of an artificial disc 24.

FIGS. 8, and 18-19B illustrate another embodiment of a connector elementfor joining the pusher rod 20 _(b) to the pusher block 18 _(b), andoptionally to a prosthesis 24 _(b). As shown in FIGS. 19A and 19B, thepusher block 18 _(b) includes a bore 401 having a proximal opening 406,a distal opening 405, and a chamber 408 extending therebetween. Theproximal and distal openings 406, 405 preferably each have substantiallythe same diameter, and preferably each have a diameter less than thediameter of the chamber 408. As shown in FIG. 19B, the proximal opening406 includes a threaded region 403 which mates to a correspondingthreaded region 411 formed on the rod 20 _(b) (FIG. 18). The proximalopening 406 can, however, include a variety of engagement elements suchas, for example, an o-ring which mates to a corresponding groove formedon the rod 20 _(b). The distal opening 405 does not include threads, andthus is effective to prevent the threaded portion of the rod 20 _(b)from being threaded through the distal opening 405. The proximal opening406 can also include a tapered portion 409 for abutting a correspondingtapered portion 410 formed on the rod 20 _(b).

FIG. 18 illustrates a pusher rod 20 _(b) that is suitable for use withthe embodiment of pusher block 18 _(b) shown in FIGS. 19A and 19B.Pusher rod 20 _(b) includes a distal tip 413, a connector segment 412extending proximally from the distal tip 413, and an annular flange 411having a distal end 418 integral with the connector segment 412 and aproximal end 416 mated to the rod 20. The proximal and distal ends 416,418 can be tapered to facilitate insertion and removal of the rod 20_(b) from the pusher block 18. The distal tip 413 of the rod 20 _(b) canmate to a prosthesis, and thus can include an engagement element. Asshown in FIG. 18, the distal tip 413 is threaded 415 to mate withcorresponding threads formed in a bore in a prosthesis.

In use, the rod 20 _(b) is inserted into the proximal opening 406 of thepusher block 18. The distal tip 413 and connector segment 412 can beinserted through the bore until the threaded annular flange 411 engagesthe threaded region 403 of the pusher block 18 _(b). The flange 411 canthen be rotated and thus threaded through the bore 403 to position theflange 411 in the chamber 408. Further distal movement of the rod 20_(b) will insert the distal tip 413 and a substantial portion of theconnector rod 412 through the distal opening 405 of the pusher block 18_(b). The lack of threads, and the size differential, in the distalopening 405 will, however, prevent the annular flange 411 from exitingthe chamber. Once the annular flange 411 is positioned in the chamber,the rod 20 _(b) is free to rotate. The rod 20 _(b) can then be rotatedto positively engage a prosthesis, or to detach the rod from aprosthesis. In an exemplary embodiment, the threads formed on theannular flange 411 are oriented in a direction opposite to the threads415 formed on the distal tip 413. This allows the rod 20 _(b) to bedetached from a prosthesis without allowing the rod 20 _(b) to bethreadingly removed through the proximal opening 406.

A person having ordinary skill in the art will appreciate that theannular flange 411, and the distal tip 413 can employ a variety ofengagement elements other than threads. For example, other lockingelements include snap-fit engagements, frictional engagements,bayonet-type locks, leur locks, or any other type of connector.

FIG. 16 illustrates another embodiment of a connector element forjoining the pusher block 18 _(d) to a prosthesis 600. As shown, agrasper element 500 is provided for grasping a prosthesis 600. Thegrasper 500 includes a proximal portion 502 and a distal portion 504.The proximal portion 502 is elongate, having a substantially cylindricalcross-section with an outer diameter d, and a bore 506 extendingtherethrough along the longitudinal axis l of the instrument. The bore506 is adapted to matingly engage the distal end 20A of the rod 20, andthus can include internal threads that threadingly receive the threadeddistal end 20A of the rod 20. A person having ordinary skill in the artwill appreciate that a variety of alternative engagement mechanisms canbe provided for mating the grasper 500 to the rod 20. The outer diameterd of the cylindrical proximal portion 502 should be less than thediameter of the bore 80 _(d) in the pusher block 18 _(d) to allow theproximal portion 502 to be inserted into the bore 80 _(d). The proximalportion 502 preferably includes a tapered region 505 which increasestoward the distal portion 504.

The distal portion 504 of the grasper 500 is oriented to extend in adirection substantially transverse to the longitudinal axis l of theinstrument and includes first and second wing-like components 508, 509,each positioned on opposed sides of the longitudinal axis l, andseparated from one another by a gap 513. The first and second components508, 509 are not attached to each other, but include a proximallyextending portion 510, 511 which mates to the proximal portion 502. Theproximally extending portions 510, 511 taper inwardly toward theproximal portion 502. As a result, the grasper 500 incrementallyincreases in diameter d toward the distal portion 504 of the grasper500. In an exemplary embodiment, the gap 513 allows the first and secondcomponents 508, 509 to be pinched together.

The first and second components 508, 509 each include a distally facingwall 520, 521. The walls 520, 521 can have a shape that conforms to theshape of a prosthesis, and preferably the walls are slightly concave tofit around a substantially cylindrical or disc-shaped prosthesis 600, asshown. Each component 508, 509 can include a protruding element 515, 516disposed on the distally facing wall 520, 521 that is effective toengage a prosthesis 600. The protruding elements 515, 516 can be, forexample, triangle-shaped, diamond shaped, or hook-like members which,when placed into openings 518 formed in the prosthesis 600, areeffective to engage the prosthesis 600.

In use, the grasper 500 is inserted into the bore 80 _(d) in the pusherblock 18 _(d) and it is mated to the rod 20. The protruding elements515, 516 are inserted into the openings 518 formed in the prosthesis600, and the rod 20 is rotated to engage the grasper 600, thereby movingthe grasper 600 proximally. As the grasper 600 is pulled in a proximaldirection by the rod 20, the tapered portion of the grasper 500 ispulled into bore 80 _(d), thereby causing the first and secondcomponents 508, 509 to be pinched together. As a result, the protrudingelements 515, 516 grasp and retain the prosthesis 600. The prosthesis600 can then be positioned between adjacent vertebrae and, oncepositioned, the rod 20 can be rotated in the opposite direction torelease the grasper 500, thereby allowing the first and secondcomponents 508, 509 to return to their separated state, thus releasingthe prosthesis 600.

In an exemplary embodiment, the pusher block 18 _(d) includes a recessedregion 19 formed in each of the side walls of the pusher block 18 _(d)to allow the grasper 500 to be inserted into the bore 80 _(d). The firstand second components 508, 509, when mated to the pusher block 18 _(d),sit within the recessed region 19. The rod 20 preferably includes a stopsurface (not shown) to prevent further insertion of the rod 20 throughthe bore 80 _(d) in the pusher block 18 _(d). The stop surface should bepositioned to allow a distal portion of the rod 20 to extend through thebore 80 _(d) to engage the grasper 500.

The depth of insertion of the cage 600 between the vertebral bodies isdependant on the length of the grasper 500 and the depth of the recessedportion 19. For example, the length of the grasper 500 and the depth ofthe recessed portion 19 can be substantially the same such that thedistal end of the pusher block is aligned with the distal end of thegrasper. In use, the distal ends of the pusher block and the grasperalign with the outer edge of the adjacent vertebrae. As a result, theimplanted disc is substantially aligned with the outer edge of theadjacent vertebrae. Alternatively, the grasper 500 can have a lengthgreater than the depth of the recessed portion 19 such that the depth ofinsertion of the disc is substantially equal to the different betweenthe length of the grasper 500 and the depth of the recessed portion 19.

FIGS. 9 and 10 illustrate an alternative embodiment in whichinstallation tool 10′ includes a locking mechanism 108 in the proximal,handle portion 12B′, 14B′ of levers 12′, 14′. The locking mechanism,which may comprise a latch and groove, simply secures the proximalhandle portion of levers in a desired position and prevents completeseparation of these elements. FIG. 9 illustrates the tool 10′ in aposition in which the proximal portion 12B′, 14B′ of the levers is openor unactuated. The locking mechanism 108 prevents further opening orseparation of the proximal portions 12B′, 14B′ of the levers. However,as shown in FIG. 10, the locking mechanism still allows the handles12B′, 14B′ to be actuated or closed together in order to operate thetool and install a prosthesis, such as artificial disc 24. One benefitof the locking mechanism 108 is that the disc is less likely to becomeinadvertently dislodged from the tool during pre-surgical installationmanipulation of the tool.

FIG. 13 illustrates an embodiment of the invention in which installationtool 300 includes a plurality protrusions 302, 304 formed on proximal orhandle portions 312B, 314B of levers 312, 314. Preferably, theprotrusions 302, 304 are formed on lateral surfaces of the handleportions. In an exemplary embodiment two protrusions are formed on eachof the top and bottom levers 312, 314. Although illustrated as beingsubstantially cylindrical in shape, it is understood that protrusions302, 304 may take virtually any shape. Referring back to FIG. 3B, forexample, the proximal end 12B, 14B of the handles 12, 14 can have aT-shape. The T-shape, or the protrusions, may be useful to facilitateextraction of the blade tips 350A, 350B using a tool such a slaphammer800 or a slap fork (shown in FIG. 17) The slap hammer 800 is positionedaround the levers 12, 14, and slid proximally to apply a proximallydirected force to the T-shaped handles, or to the protrusions 302, 304.The dimensions of T-shaped handles or the protrusions 302, 304 may varywithin a wide range. Generally, however, the T-shaped handles orprotrusions 302, 304 extend from the lateral surfaces of levers 312, 314by a distance of about 3 mm to 50 mm.

Although T-shaped handles and protrusions 302, 304 are illustrated, oneof ordinary skill in the art will readily appreciate that the handlescan have a variety of configurations for allowing use of a slap hammerwith the instrument.

With reference to FIGS. 13-15B, the installation tool 300 may alsoinclude a feature which permits selective adjustment of blade tip length(i.e., the distance between the distal end 306 of blade tips 350A, B andstop surface 354). In such an embodiment the distal portion of each ofthe levers 312A, 314A has a stop member component 307 and a blade membercomponent 308, which are longitudinally separable with respect to eachother. The separability of components 307 and 308 permits the blade tiplength to be adjusted by varying the relative positions of components307, 308.

As shown in FIGS. 13 and 14 tool 300 includes a junction box 309 whichhouses and secures the components 307, 308. A portion 307A of the stopmember component 307, which mates with the inner surface of the cover320 of the junction box 309, includes a series of grooves 310 separatedby raised ridges 311. Similarly, the abutting, inner surface of thecover 320 of the junction box 309 includes grooves and ridges 310, 311as well. As further illustrated, the cover 320 is secured to levers 312,314 by suitable fasteners, such as screws 322. Biasing elements, such ascompression springs (not shown) are preferably used to bias the junctionbox to a position such that the grooves and ridges 310, 311 of the cover320 and the stop member component 307 mate with and remain firmlysecured to one another. As shown in FIG. 14, suitable indicia 325 may bepresent on the stop member component 307 to indicate the position of thestop member component 307 with respect to the blade member component.Although FIG. 14 only illustrates, in detail, the configuration of lever12, it is understood that the same construction is used for lever 14.

The result of this selective adjustability is shown in FIGS. 15A and15B, in which the blade tip length is greater in FIG. 15A than in FIG.15B.

FIGS. 1 and 8A-8D sequentially illustrate the use of tool 10 for theinstallation of an artificial disc 24. The tool is first assembled asshown in FIG. 1, and with pusher block 18 positioned in its initialposition such that its proximally facing wall 96 abuts shoulder 26, theposterior surface 27 of the disc is placed against the distal facingwall 97 of the pusher block. With the handles 12B, 14B in the openposition and the blade tips 50A, B closed, the blade tips are wedgedbetween adjacent vertebral bodies 201, 202 to effect slight separationbetween at least the anterior portions of the vertebral bodies. Theblade tips 50A, B should be fully inserted between the vertebral bodies,as shown in FIG. 8A, so as to enable the vertebral stop surface 54 toabut the posterior side 204 of the vertebral bodies 201, 202. The pusherrod 20 is then pushed forward, causing distal movement of the pusherblock 18 and artificial disc 24. The forward or distal movement ofpusher block 18 and the artificial disc 24 also causes furtherseparation of the blade tips 50A, B and thus further separation of thevertebral bodies 201, 202 as shown in FIG. 8B. Advancement of the pusherblock 18 and the artificial disc 24 continues until, as shown in FIG.8C, the disc is properly installed between adjacent vertebral bodies.FIGS. 8B and 8C illustrate that at all times separation of the vertebralbodies is only effected to the extent necessary to insert the disc.Excessive distraction or separation of the vertebral bodies does notoccur because the separation of vertebral bodies is caused by the heightof the pusher block.

The installation tool of the present invention can also be provided as akit having modular components which allow the surgeon to select fromamong a variety of components to assemble an installation tool that isoptimized for its intended use. The kit preferably includes severaldifferent rods, pusher blocks, and connectors elements, such as grasper500, each adapted to be used with a particular implant. For example, thekit can include three types of pusher blocks, each adapted to mate witha particular prosthesis. As shown in FIG. 16, the pusher block 18 _(d)can be used in combination with grasper 500 to insert a cage-typespacing prosthesis. Alternatively, as shown in FIG. 1, pusher block 18can be provided for inserting an artificial disc. A person havingordinary skill in the art will appreciate that the installation tool caninclude a variety of components having a combination of differentfeatures. Moreover, the components can be adapted for use withparticular types of prosthesis, or for use with other components.

One of ordinary skill in the art will appreciate further features andadvantages of the invention based on the above-described embodiments.Accordingly, the invention is not to be limited by what has beenparticularly shown and described, except as indicated by the appendedclaims. All publication and references cited herein are expresslyincorporated herein by reference in their entity.

What is claimed is:
 1. A medical device installation kit, comprising: apair of opposed levers, each lever having a proximal handle portion anda distal portion; a fulcrum disposed between the opposed levers forallowing pivotal movement of the levers with respect to each other; anda plurality of prosthesis installation assemblies adapted to be slidablydisposed between the levers and slidably coupled to the fulcrum suchthat each prosthesis installation assembly is movable between a first,proximal position and a second, distal position, each assembly includinga handle portion effective to move the prosthesis installation assemblybetween the first and second positions, and a distal prosthesiseffecting element adapted to place a prosthesis between adjacent bonestructures.
 2. The medical device installation kit of claim 1, whereinone of the prosthesis installation assemblies comprises: a pusher blockhaving a proximal end, a distal end, and a bore extending therethrough;a pusher rod slidably disposed between the levers and extending throughthe bore in the pusher block; and a grasping element effective toreleasably engage a prosthesis.
 3. The medical device installation kitof claim 2, wherein the grasping element has an elongate proximalportion adapted to fit within the bore of the distal end of the pusherblock, and a distal portion having opposed first and second componentswhich are movable between a first, open position, and a second, closedposition that is effective to engage a prosthesis.
 4. The medical deviceinstallation kit of claim 3, wherein a distal end of the rod threadinglyengages the bore of the pusher block and wherein rotation of the rod ina first direction is effective to cause the elongate proximal portion ofthe grasping element to move proximally within the bore of the pusherblock and move the first and second components to the second, closedposition while rotation of the rod in a second direction is effective tocause the elongate proximal portion of the grasping element to movedistally out of the bore of the pusher block and move the first andsecond components to the first, open position.
 5. The medical deviceinstallation kit of claim 1, wherein one of the prosthesis installationassemblies comprises a pusher rod having a proximal handle portion, anddistal portion having a distal tip adapted to positively engage aprosthesis.
 6. The medical device installation kit of claim 5, whereinthe prosthesis installation assembly further includes a pusher blockhaving a proximal end, a distal end, and a bore extending therethrough,the distal portion of the pusher rod extending through the bore in thepusher block.
 7. The medical device installation kit of claim 1, whereinone of the prosthesis installation assemblies comprises: a pusher rodhaving an externally threaded first distal portion and an externallythreaded second distal portion, the second distal portion having adiameter greater than a diameter of the first distal portion and beingpositioned proximal to the first distal portion; a pusher block having abore extending entirely therethrough having a threaded proximal openingthat is threadingly matable with the second distal portion of the rod,and a distal opening having a diameter less than the diameter of thesecond distal portion of the rod; and a chamber disposed between theproximal and distal openings and having a diameter greater than thediameter of the second distal portion of the rod.
 8. The medical deviceinstallation kit of claim 7, wherein the rod is freely rotatable whenthe second distal portion is disposed within the chamber of the pusherblock.
 9. The medical device installation kit of claim 8, wherein thefirst distal portion of the rod is adapted to positively engage aprosthesis.
 10. The medical device installation kit of claim 1, whereinone of the prosthesis installation assemblies comprises: a pusher blockhaving a proximal end, a distal end, and a bore extending therethrough,the pusher block being slidably disposed between the levers; a pusherrod having a proximal, handle portion and a distal portion extendingthrough the bore in the pusher block; and a plurality of connectorelements having a proximal portion adapted to mate to a distal tip ofthe pusher rod and a distal portion adapted to mate to a prosthesis. 11.A medical device installation tool, comprising: a pair of opposedlevers, each having a proximal, handle portion and a distal portion; afulcrum disposed between the two levers and including an openingextending therethrough; a pusher block having a proximal end, a distalend, and a bore extending at least partially therethrough, the pusherblock being positioned between the two levers and slidably moveablebetween an initial location distal of the fulcrum and a final locationadjacent a distal end of the levers; and a pusher rod having a proximal,handle end, and a distal end, the pusher rod being slidably disposedthrough the fulcrum and the distal end of the pusher rod extending intothe bore in the pusher block.
 12. The medical device installation toolof claim 11, wherein the bore is a blind bore and the distal end of thepusher rod mates with the blind bore in the pusher block.
 13. Themedical devise installation tool of claim 11, wherein each leverincludes a surface feature disposed between the proximal and distalportions thereof, the surface feature being effective to slidably mateto a complementary surface feature formed in a prosthesis.
 14. Themedical device installation tool of claim 11, wherein the bore extendsentirely through the pusher block and the distal end of the pusher rodhas a distal tip that is adapted to extend through the bore in thepusher block and that is effective to mate to a prosthesis.
 15. Themedical device installation tool of claim 14, wherein the pusher blockhas a height effective to separate the levers from a prosthesis suchthat, when the pusher rod is mated to a prosthesis, the levers arespaced apart from the prosthesis.
 16. The medical device installationtool of claim 14, wherein the rod includes an externally threaded firstdistal portion and an externally threaded second distal portion, thesecond distal portion having a diameter greater than a diameter of thefirst distal portion and being positioned proximal to the first distalportion.
 17. The medical device installation tool of claim 16, wherein:the bore of the pusher block includes a threaded proximal opening thatis threadingly matable with the second distal portion of the rod; adistal opening of the pusher block having a diameter less than thediameter of the second distal portion of the rod; and a chamber disposedbetween the proximal and distal openings, the chamber having a diametergreater than the diameter of the second distal portion of the rod. 18.The medical device installation tool of claim 17, wherein the rod isfreely rotatable when the second distal portion is disposed within thechamber of the pusher block.
 19. The medical device installation tool ofclaim 17, wherein the threaded first distal portion of the rod isthreaded in a direction opposite to the direction of the threads of thethreaded second distal portion.
 20. The medical device installation toolof claim 11, wherein the bore extends entirely through the pusher blockand a distal tip of the pusher rod is adapted to extend through the borein the pusher block, the distal tip of the pusher rod being furtheradapted to mate to a grasping element effective to releasably engage aprosthesis.
 21. The medical device installation tool of claim 20,further comprising a grasping element that has an elongate proximalportion with a bore formed therein and a distal portion that iseffective to releasably engage a prosthesis, the proximal portion havingan outer diameter that is adapted to fit within the bore of the distalend of the pusher block.
 22. The medical device installation tool ofclaim 21, wherein the distal portion of the grasping element includesopposed first and second components that are movable between a first,open position, and a second, closed position that is effective to engagea prosthesis.
 23. The medical device installation tool of claim 22,wherein the distal end of the rod threadingly engages the bore of thegrasping element, and wherein rotation of the rod in a first directionis effective to cause the elongate proximal portion of the graspingelement to move proximally within the bore of the pusher block and movethe first and second components to the second, closed position whilerotation of the rod in a second direction is effective to cause theelongate proximal portion of the grasping element to move distally outof the bore of the pusher block and move the first and second componentsto the first, open position.
 24. The medical device installation tool ofclaim 23, wherein the first and second components each include at leastone surface feature effective to engage a prosthesis.
 25. The medicalinstallation tool of claim 11, wherein the bore extends entirely throughthe pusher block and a distal tip of the pusher rod is adapted to extendthrough the bore in the pusher block, the distal tip of the pusher rodbeing further adapted to positively engage a prosthesis.
 26. The medicaldevice installation tool of claim 11, wherein the pusher block has upperand lower recesses, each adapted to seat one of the levers, each of theupper and lower recesses including opposed, substantially vertical wallsseparated by a substantially horizontal base wall, the vertical wallseach including a rail extending between the proximal and distal ends ofthe pusher block and effective to retain the levers.
 27. The medicaldevice installation tool of claim 11, wherein the handle portion of eachlever is substantially T-shaped.
 28. The medical device installationtool of claim 11, wherein the pusher rod includes a stop membereffective to limit advancement of the pusher rod through the opening inthe fulcrum.
 29. The medical device installation tool of claim 11,wherein the distal portion of each lever includes a curve tip.
 30. Amedical device installation tool, comprising: a pair of opposed leversmovable at a distal end thereof relative to one another between a closedposition and an open position; a pusher block positioned between thepair of opposed levers and being movable between a proximal location anda location adjacent to the distal end of the pair of opposed levers, thepusher block including projections that slide within respective tracksformed in the pair of opposed levers as the projections advance distallywith the pusher block; and a pusher rod disposed between the pair ofopposed levers and having a distal end that is coupled to the pusherblock.
 31. The tool of claim 30, wherein the projections comprise aplurality of posts extending from the pusher block, each post beingcomplementary to a track formed in each lever such that the post isconfigured to slide along the track to facilitate movement of the pusherblock with respect to the opposed levers.
 32. The tool of claim 30,wherein at least one of the opposed levers includes a stop featurelocated on a distal portion thereof and configured to engage a vertebralbody to stop further distal movement of the opposed levers.
 33. The toolof claim 32, wherein the stop feature comprises a vertically oriented,distally facing surface located on the distal portion of at least one ofthe opposed levers.
 34. The tool of claim 30, wherein the pusher rod isconfigured to advance the pusher block distally towards the distal endsof the opposed levers.
 35. The tool of claim 30, wherein the pusherblock includes a bore formed therein for receiving a distal end of thepusher rod.
 36. The tool of claim 30, wherein the pusher block includesa recessed region adapted to nest an implant.
 37. The tool of claim 36,wherein the recessed region includes a concave, arcuate contact wall.38. A medical device installation system, comprising: first and secondopposed levers being movable at a distal end thereof between a closedposition and an open position, each lever having an inwardly facingsurface upon which an implant can ride; a pusher block positionedbetween the first and second opposed levers and configured to distallyadvance an implant, the pusher block having vertical sidewalls thatdefine an upper recess in which the first lever slides and a lowerrecess in which the second lever slides during distal advancement of thepusher block to maintain alignment between the pusher block and thefirst and second levers; and an implant having a first groove formed inan upper surface of the implant that receives a portion of the firstlever and a second groove formed in a lower surface of the implant thatreceives a portion of the second lever.
 39. The system of claim 38,wherein the first and second levers have a T-shaped profile.
 40. Thesystem of claim 38, wherein at least one of the opposed levers includesa stop feature located on a distal portion thereof and configured toengage a vertebral body to stop further distal movement of the opposedlevers.
 41. The system of claim 40, wherein the stop feature comprises avertically oriented, distally facing surface located on the distalportion of at least one of the opposed levers.
 42. The system of claim38, further comprising a pusher rod extending proximally from the pusherblock and configured to advance the pusher block distally towards thedistal ends of the first and second levers.
 43. The system of claim 38,wherein the pusher block includes a recessed region adapted to nest theimplant.
 44. The system of claim 38, wherein the recessed regionincludes a concave, arcuate contact wall.
 45. The system of claim 38,wherein the pusher block includes a grasper having first and secondwings movable towards one another to grasp the implant when the implantis disposed therebetween.
 46. The system of claim 45, wherein the firstand second wings each include a hook configured to fit within a recessformed in the implant to grasp and retain the implant.